Epstein Barr virus (EBV) is a gammaherpes virus that is associated with multiple human malignancies including Burkitt's lymphoma, nasopharyngeal carcinoma, Hodgkin's disease, some non-Hodgkin's lymphomas, and B cell lymphomas in bone marrow and solid organ recipients and patients with AIDS. In immunosuppressed and immunocompromised individuals the prevailing view is that impaired cellular immunity permits uncontrolled expansion of EBV-infected B cells. However, alterations in EBV-infected B cells that provide growth and survival advantages could also contribute to lymphomagenesis. Accordingly, we have demonstrated that EBV-infected B cell lines established from patients with post-transplant lymphoproliferative disorder (LPD) have constitutive activation of the Jak/STAT signal transduction pathway that is associated with cytokine-mediated cellular growth. In addition, the EBV-infected B cell lines show marked resistance to induction of apoptosis through the Fas/Fas ligand and TRAIL/DR pathways. Importantly, establishment of a latent EBV infection is sufficient to confer resistant to previously sensitive cells. Moreover, resistance to Fas-induced apoptosis correlates with expression of the natural LMP1 variants associated with increased AP-1 activation. The long-term objectivity of this work is to understand how EBV promotes the growth and survival of EBV-associated B cell lymphomas. The hypothesis is that natural LMP1 variants have differential ability to modulate pathways of apoptosis. Further, we hypothesize that LMP1 associates with Jak kinases and is sufficient for STAT activation and IL-10 production. Specific Aim 1 will determine the capacity of natural LMP1 variants to protect from intrinsic and extrinsic apoptotic stimuli. The ability of LMP1 variants to activate NFKappaB, AP-1 and modulate death receptor proximal and downstream regulators of apoptosis will be determined. Specific Aim 2 will determine the role of LMP1, and its natural variants, in activation of the Jak/STAT pathway and IL-10 expression. Elucidation of the pathways of cell death and survival in EBV-infected B cells will provide opportunities for the rational design of new therapeutics to treat EBV+ B cell lymphomas.